Macular dystrophies and degenerations are one of the most common causes of blindness. Recently, three independent mutations in elongase of very long chain fatty acids-4 (ELOVL4) have been linked to Stargardt disease-3 (STGD3), a juvenile-onset dominant macular degeneration. A mouse model of this disease, heterozygous Stgd3 mice, reproduces principal features of the human pathology: lipofuscin accumulation and reduced visual functions. The mutated gene, containing a human pathogenic 5-bp deletion, codes for a truncated Elovl4 protein which can either be inactive in lipid synthesis and/or harmful to photoreceptors. Since our heterozygous Stgd3 mice show no signs of cellular stress in the retina, we propose a pathogenic mechanism involving changes in retinal lipids. Thus the focus of the proposed studies will be on (i) identification of the currently unknown Elovl4 lipid products and determining both the (ii) physiological and (ii) pathophysiological roles of the Elovl4 lipid products in the retina. Support for lipid deficiency as a factor in STGD3 pathology is provided by studies in Stgd3 mice. The homozygous Stgd3 mice die shortly after birth with a defective skin barrier. Initial lipid analysis revealed a complete absence of the critical skin barrier acylceramide lipids, and suggested that the direct products of Elovl4 may be very long chain C30-C40 fatty acids, acylceramide constituents. Retinas in neonatal animals are immature and thus to further define the Elovl4 products we will continue lipid analysis in other Elovl4-expressing tissues of neonatal homozygous Stgd3 mice and in the retina of adult heterozygous Stgd3 mice. The lipids will be analyzed using thin layer chromatography and high pressure liquid chromatography combined with mass spectrometry. To study the effects of deficiency of the Elovl4 lipid products in mature retina we will use the loxP-Cre system to generate mice with photoreceptor-specific Elovl4-knockout. Their retinas will be subject to structural, functional and biochemical studies using microscopy, electroretinography, as well as lipid and protein analysis. The results of these analyses will confirm the identity of, and reveal the roles of Elovl4 lipid products in retinal physiology and pathology. These findings will help in an understanding of the pathogenesis of STGD3 and may suggest new approaches for preventing vision loss in humans.